1. Field of the Invention
The present invention relates to a battery in which a terminal is provided for a lid plate covering a top opening of a battery container containing a power generating element.
2. Description of the Related Art
FIG. 7 shows an attachment structure of a terminal for a conventional large-sized nonaqueous electrolyte secondary battery (see FIG. 6 to FIG. 8 in JP-A-2001-357833, for example). This nonaqueous electrolyte secondary battery is configured such that an elliptic cylindrical winding power generating element 2 is contained within a battery container 1 and a top opening of the battery container 1 is covered and sealed by a lid plate 3. At both right and left ends of the power generating element 2, metallic foils 2a, 2a of electrodes respectively protrude in a wound state. These metallic foils 2a, 2a are connected to current collecting connectors 5, 5. Further, to both right and left ends of the lid plate 3, external terminals 4, 4 are attached.
The external terminal 4 is configured such that a bolt portion 4b is disposed projecting upward from an upper surface of a low and columnar base portion 4a, and a tube 4c is disposed projecting downward from a lower surface of the base portion 4a. Further, the tubes 4c, 4c of the external terminals 4, 4 respectively on a positive electrode side and a negative electrode side are fitted into the battery container 1 over the lid plate 3, respectively through through holes of external insulating and sealing members 6, 6 provided on an upper surface of the lid plate 3 at both right and left ends, terminal pull-out through holes 3a, 3a at the both right and left ends of the lid plate 3, and through holes of internal insulating and sealing members 7, 7 provided on a lower surface of the lid plate 3 at the both right and left ends. The tubes 4c, 4c are also swaged from below respectively through through holes provided in connecting portions 5a, 5a of the current collecting connectors 5, 5 that are bent in a horizontal direction. Therefore, each external terminal 4 is configured such that the tube 4c is connected to the current collecting connector 5 by the caulking, as well as to the metallic foil 2a of the electrode of the power generating element 2, and fixedly attached to the lid plate 3 in an insulated and sealed state as the lid plate 3 is held between the insulating and sealing members 6 and 7.
However, according to such an attachment structure of the external terminal 4, when a pressure-bonded terminal of a lead wire or the like is fitted into the bolt portion 4b of the external terminal 4 and fastened by a nut or the like in order to connect the nonaqueous electrolyte secondary battery to an external device, in particular when such a nut is repeatedly attached and detached, there is a possibility that fastening torque is directly applied to the portion of the tube 4c to make the caulking between the tube 4c and the connecting portion 5a of the current collecting connector 5 loose, and only the external terminal 4 possibly runs idle. The external terminal 4 running idle causes a problem of reduced battery performance due to an increased contact electrical resistance between the external terminal 4 and the current collecting connector 5, as well as a problem of defective sealing within the battery container 1 due to a gap occurring between the insulating and sealing members 6 and 7.
In addition, as aluminum alloy is often used for the external terminal 4 on the positive electrode side in the case of the nonaqueous electrolyte secondary battery, there is another problem that when the bolt portion 4b is tightly fastened by a nut or the like, or when such a nut is repeatedly attached and detached, a thread ridge of the bolt portion 4b is often damaged.
Accordingly, there have conventionally been proposed to provide the base portion 4a of the external terminal 4 in a polygonal columnar shape having a square or hexagonal transverse section, to provide an external terminal recessed portion of a corresponding shape for the external insulating and sealing member 6, and to have the base portion 4a be fitted into the external terminal recessed portion of the external insulating and sealing member 6, thereby baffling the external terminal 4 (see FIG. 1 to FIG. 5 of JP-A-2001-357833, for example).
However, even with such an attachment structure of the external terminal 4, there is a problem that the external terminal 4 possibly runs idle by a small amount of angle due to a small gap in the fitting between the base portion 4a and the external terminal recessed portion of the external insulating and sealing member 6, and it is not possible to completely prevent the caulking between the tube 4c and the connecting portion 5a of the current collecting connector 5 from becoming loose. In addition, there is another problem that when the bolt portion 4b is fastened by a nut or the like, the fastening torque is directly applied to the external insulating and sealing member 6 to apply a significant stress to the external insulating and sealing member 6, and whereby airtightness become impaired.
For this reason, conventionally, an attachment structure of the external terminal 4 as shown in FIG. 8 has also been proposed (see JP-A-2003-346774 (page 2 and FIG. 3), for example). According to the external terminal 4 of this example, the base portion 4a is provided in a hexagonal columnar shape, and the bolt portion 4b is disposed projecting from the upper surface of the base portion 4a, but a tube is not disposed projecting from the lower surface. Further, an external terminal recessed portion 6a of a similarly hexagonal shape is provided in an upper surface of the external insulating and sealing member 6, and the base portion 4a is fitted into the external terminal recessed portion 6a, thereby attempting to baffle the external terminal 4.
The upper surface of the external insulating and sealing member 6 is also provided with an auxiliary terminal recessed portion 6b, into which a base portion 8a of an auxiliary terminal 8 is fitted. The auxiliary terminal 8 is configured such that a first tube 8b is disposed projecting downward from a lower surface of the base portion 8a, and a second tube 8c is disposed projecting upward from an upper surface of the base portion 8a. Further, the first tubes 8b, 8b of the auxiliary terminals 8, 8 of the positive electrode side and the negative electrode side are fitted into the battery container 1 over the lid plate 3, respectively through through holes provided in bottom surfaces of the auxiliary terminal recessed portions 6b, 6b of the external insulating and sealing members 6, 6, the terminal pull-out through holes 3a, 3a at the both right and left ends of the lid plate 3, and the through holes of the internal insulating and sealing members 7, 7. The first tubes 8b, 8b are also swaged from below respectively through through holes provided in the connecting portions 5a, 5a of the current collecting connectors 5, 5. Therefore, each auxiliary terminal 8 is configured such that the first tube 8b is connected to the metallic foil 2a of the power generating element 2 through the connecting portion with the connecting portion 5a of the current collecting connector 5 by the swaging, and fixedly attached to the lid plate 3 in an insulated and sealed state as the lid plate 3 is held between the insulating and sealing members 6 and 7.
Further, a connecting conductor 9 is attached to the second tube 8c of the auxiliary terminal 8 and the bolt portion 4b of the external terminal 4. The connecting conductor 9 is a substantially rectangular plate member, in which a hole 9a is provided in one end, and a terminal through hole 9b is provided in the other end. Further, the connecting conductor 9 is configured such that the bolt portion 4b of the external terminal 4 is inserted into the terminal through hole 9b from below, and the second tube 8c of the auxiliary terminal 8 is inserted into the hole 9a from below, and swaged from above. Therefore, when the bolt portion 4b is fastened by a nut or the like in order to connect to the external device, the external terminal 4 is connected and fixed to the auxiliary terminal 8 through the connecting conductor 9, and thus connected to the metallic foil 2a of the electrode of the power generating element 2.
By using such an attachment structure of the external terminal 4, as the fastening torque is not directly applied to the auxiliary terminal 8 even when the bolt portion 4b is fastened by a nut or the like, the swaging between the auxiliary terminal 8 and the connecting portion 5a of the current collecting connector 5 may not become loose. In addition, even in the case of the nonaqueous electrolyte secondary battery, it is possible to use aluminum alloy only for the auxiliary terminal 8 on the positive electrode side, and iron or steel having high strength can be used for the external terminal 4. Therefore, the thread ridge of the bolt portion 4b may not be damaged due to fastening by a nut or the like.
Conventionally, there is proposed a technique for baffling the external terminal by providing a projecting portion for the base portion of the external terminal, and inserting the projecting portion into a recessed hole of a lid plate portion made of resin (see JP-A-10-125291, for example). However, in this case, the base portion of the external terminal is within the battery container, and the recessed hole is also defined in the lower surface within the lid plate portion. Therefore, it is necessary that the attachment of the external terminal and the insertion of the projecting portion into the recessed hole be carried out within the battery container, posing a problem that the battery assembly is difficult.
However, as a result of a great deal of consideration, there is a problem even in the attachment structure of the external terminal 4 as described above that as the fastening torque is directly applied to the external terminal recessed portion 6a of the external insulating and sealing member 6 when the bolt portion 4b is fastened by a nut or the like, a significant stress is applied by to the external insulating and sealing member 6 that seals between the auxiliary terminal 8 and the lid plate 3 by swaging the first tube 8b of the auxiliary terminal 8, and therefore it is not possible to prevent high level of airtightness from being impaired. Specifically, as the external insulating and sealing member 6 is pressed strongly by the upper surface of the lid plate 3, as well as subjected to a large strength in a twisted direction, slight deformation of the material generates a minor gap in an interface with the lid plate 3 and possibly makes the sealing defective. Further, as the external insulating and sealing member 6 is baffled with respect to the lid plate 3, the external insulating and sealing member 6 itself is possibly displaced slightly due to a slight gap between the baffling and the lid plate 3, and whereby a minor gap is generated in the interface with the lid plate 3 and possibly makes the sealing defective.